A method for predicting denitrification performance of a layered biological retention facility

Abstract

The application discloses a method for predicting denitrification efficiency of a layered biological retention facility, which comprises the following steps: 1, setting a plurality of infiltration subunits in series in AQUASIM software, and using a convection-dispersion equation to simulate the infiltration process of nitrogen pollutants in rainwater in the biological retention facility; 2, setting an adsorption kinetics equation, carbon release kinetics equation and nitrogen release kinetics equation in the corresponding subunits; 3, connecting a complete mixing reaction unit in series at the water outlet end of the last-stage subunit; 4, inputting the characteristic parameters of the biological retention facility, the adsorption characteristic parameters, the water inflow Q of the facility and the water pollutant concentration, the nitrogen concentration accumulated in the last rainfall, and solving the denitrification condition of the facility at the end of the rainfall by using the AQUASIM software; and 5, establishing a second complete mixing reaction unit to simulate the nitrogen degradation process of microorganisms in the dry period. The application can accurately predict the denitrification efficiency of the layered design biological retention facility, and provides a basis for the optimized design of the biological retention facility.

Description

Technical Field

[0001] This invention relates to a bioretention facility, belonging to the field of rainwater treatment technology, and specifically to a method for predicting the denitrification efficiency of a stratified bioretention facility. Background Technology

[0002] Urban non-point source pollution has become one of the most challenging aspects of comprehensive water environment management in my country. Nitrogen and phosphorus pollutants accumulated on urban surfaces are leached into receiving water bodies by rainfall and runoff, contributing significantly to eutrophication. Bioretention facilities are a widely used runoff pollution source control measure in sponge city construction. These facilities not only reduce peak runoff flow and delay its arrival time but also effectively remove suspended solids, organic matter, and heavy metals from runoff. However, bioretention facilities have a relatively weak capacity for removing dissolved nitrogen and phosphorus pollutants, and under some extreme rainfall conditions, these pollutants may even leach out.

[0003] To improve the nitrogen removal performance of bioretention facilities, researchers have optimized the design of traditional facilities using various techniques, including changes in packing materials, structure, and inlet / outlet methods. Setting up a submerged zone of a certain depth at the bottom of the bioretention facility not only provides internal rainwater retention space but also maintains an anoxic environment during the dry season, thus promoting denitrification. Given the scarcity of organic carbon sources in rainwater, adding solid organic carbon sources to the submerged zone of the bioretention facility can further enhance its nitrogen removal efficiency. However, different solid organic carbon sources have significantly different carbon release rates, which can lead to problems such as organic carbon leaching or decreased nitrogen removal efficiency. Using inorganic electron donors (pyrite) to replace solid organic carbon sources as an improved packing material in the submerged zone can effectively promote autotrophic denitrification, achieving simultaneous nitrogen and phosphorus removal while avoiding the problems of organic carbon or nitrogen and phosphorus leaching. However, the electron donation rate of pyrite is much lower than that of solid organic carbon sources, making it difficult to meet the nitrogen removal requirements under conditions of high pollution loads, high runoff, and short-interval continuous rainfall. Adding biochar to the non-submerged zone of a bioretention facility can effectively enhance the adsorption capacity of the packing material for hydrophobic organic matter and ammonia nitrogen, and improve the water holding capacity of the non-submerged zone. This will help block oxygen diffusion and expand the denitrification zone of the facility. In summary, a stratified optimization design for bioretention facilities can maximize their nitrogen removal potential.

[0004] Because bioretention facilities are a passive treatment technology, their denitrification performance is also affected by a range of rainfall and underlying surface conditions, such as rainfall amount, duration, drought period, and influent nitrogen load. In the sponge city design phase, existing technologies lack a simulation method to predict the denitrification efficiency of proposed bioretention facilities and to optimize their design based on local climate conditions and underlying surface characteristics, thereby achieving the goal of efficiently utilizing bioretention facilities to purify surface rainwater.

[0005] The "denitrification efficiency" mentioned in this patent application refers to the nitrogen removal rate of the bioretention facility in the influent. Summary of the Invention

[0006] In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a method for predicting the nitrogen removal efficiency of a stratified bioretention facility. This method can calculate the nitrogen removal rate in the effluent of the stratified bioretention facility under different operating conditions, and provide a basis for optimizing the parameters of the bioretention facility.

[0007] The technical problem to be solved by the present invention is achieved through the following technical solution, which includes the following steps:

[0008] Step 1: Based on the stratification and flooding height of the bioretention facility, set up several in-series infiltration sub-units in the AQUASIM software, and use the convection-diffusion equation to simulate the infiltration process of nitrogen pollutants in rainwater within the bioretention facility.

[0009] Step 2: Based on the adsorption characteristics of nitrogen pollutants by each packing material in the bioretention facility, adsorption isotherms and diffusion control equations are set in the corresponding sub-units to simulate the dynamic adsorption process of nitrogen pollutants by the packing material. Based on the characteristics of each packing material in releasing organic carbon and nitrogen, carbon release and nitrogen release kinetic equations are set in the corresponding sub-units to simulate the carbon release and nitrogen release process of the packing material.

[0010] Step 3: Connect a fully mixed reaction unit in series at the outlet of the last sub-unit to receive the water and nitrogen pollutants discharged from the bioretention facility during the entire rainfall process.

[0011] Step 4: Input the characteristic parameters of the bioretention facility, including cross-sectional area A, packing density ρ, packing porosity θ, usage ratio of each packing material, height of each packing layer, adsorption characteristic parameters of each packing material for nitrogen pollutants, influent flow rate Q and nitrogen pollutant concentration, and nitrogen pollutant concentration accumulated in the packing material during the previous rainfall. Use AQUASIM software to solve for the spatiotemporal variation of nitrogen pollutants in the bioretention facility and the average nitrogen concentration in the effluent under the set rainfall duration.

[0012] Preferably, the method further includes step 5: establishing a second completely mixed reaction unit for the submerged area of ​​the bioretention facility, and setting up the Michaelis-Menten equation and first-order reaction kinetic equation to simulate the nitrogen degradation process of microorganisms under anoxic conditions. Using the average concentration of nitrogen pollutants in the submerged area obtained in step 4 as the initial value of the variable, the concentration change of nitrogen pollutants in the submerged area of ​​the bioretention facility during the drought period is calculated using AQUASIM software.

[0013] This invention establishes multiple infiltration units connected in series and flexibly sets the dynamic equations of the infiltration sub-units according to different improvement methods for each layer of packing. Furthermore, it can calculate the denitrification efficiency of the bioretention facility under different operating conditions using a series of rainfall parameters and underlying surface parameters as independent variables.

[0014] The technical effects of this invention are:

[0015] 1. This invention includes the adsorption and desorption processes, carbon and nitrogen release processes, and microbial degradation processes during the rainy season in bioretention facilities, while also considering the impact of the nitrogen load accumulated in the previous rainfall on the next rainfall. Therefore, this invention can accurately predict the nitrogen removal status of bioretention facilities.

[0016] 2. This invention can adjust the characteristic parameters of the bioretention facility (such as cross-sectional area A, packing density ρ, packing porosity θ, usage ratio of each packing, height of each packing layer, etc.), packing adsorption parameters, and packing carbon release rate, etc., to simulate the denitrification efficiency of the bioretention facility under corresponding conditions. Based on the clear runoff volume and pollutant control targets, it provides a basis for the optimized design of the bioretention facility.

[0017] 3. This invention can simulate the denitrification efficiency of bioretention facilities under different influent flow rates Q, different rainfall durations, and different influent concentrations based on rainfall and underlying surface pollution conditions, providing comprehensive guidance on the scope of application of bioretention facilities in the planning and design of sponge city construction. Attached Figure Description

[0018] The accompanying drawings of this invention are described below:

[0019] Figure 1 A schematic diagram of a layered bioretention facility structure according to an embodiment of the invention;

[0020] Figure 2 This is a graph showing the change in pollutant concentration with the depth of the bioretention facility's flood layer at the end of rainfall.

[0021] (a) Nitrates; (b) Dissolved organic carbon (DOC);

[0022] Figure 3A diagram illustrating the microbial degradation process of pollutant concentrations in the submerged layer of a bioretention facility during a drought period;

[0023] (a) The influent pollutant concentration is low; (b) The influent pollutant concentration is medium; (c) The influent pollutant concentration is high.

[0024] Figure 4 To predict the treatment effect of bioretention facilities under different influent concentrations and different rainfall conditions;

[0025] (a) Nitrate removal at three different influent concentrations; (b) Nitrate removal at different rainfall levels. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0027] The AQUASIM software used in this application is an open-source software for simulating various water systems. Developed in C++, it can solve complex mathematical models composed of nonlinear ordinary differential equations or partial differential equations. AQUASIM provides seven modeling modules: mixed reactor compartment, biofilm reactor compartment, advective-diffusive reactor compartment, saturated soil column compartment, river system, lake system, and sediment system.

[0028] The method for predicting the nitrogen removal efficiency of stratified bioretention facilities provided by this invention comprises the following steps:

[0029] Step 1: Based on the stratification and flooding height of the bioretention facility, set up several in-series infiltration sub-units in the AQUASIM software, and use the convection-diffusion equation to simulate the infiltration process of nitrogen pollutants in rainwater within the bioretention facility.

[0030] According to the literature "A numerical transport model for oxygen-and nitrate-based respiration linked to substrate and nutrient availability in porous media", Widdowson, Mark A.; Molz, Fred J.; Benefield, Larry D, Water Resources Research (1988), 24(9), 1553–1565, the convection-dispersion equation is as follows:

[0031]

[0032] In the formula, C i Dissolved nitrogen concentration in rainwater (mg / m³) 3 ); x is the depth of the bioretention facility packing layer (m); ν is the average pore water velocity (m / h); D is the fluid dispersion coefficient (m). 2 / h).

[0033] The infiltration process is calculated for each infiltration subunit, and the movement of rainwater in each infiltration subunit is continuous.

[0034] Step 2: Based on the adsorption characteristics of nitrogen pollutants by each packing material in the bioretention facility, adsorption isotherms and diffusion control equations are set in the corresponding sub-units to simulate the dynamic adsorption process of nitrogen pollutants by the packing materials. Based on the characteristics of each packing material in releasing organic carbon and nitrogen, carbon release and nitrogen release kinetic equations are set in the corresponding sub-units to simulate the carbon release and nitrogen release process of the packing materials.

[0035] According to the literature "Isotherm models for adsorption of heavy metals from water - A review", Xinyu Chen, Md Faysal Hossain, Chengyu Duan, Jian Lu, Yiu Fai Tsang, Md Shoffikul Islam, Yanbo Zhou. Chemosphere, 2022, 307:135545, the adsorption isotherms mentioned include, but are not limited to, the Freundlich isotherm.

[0036] S i =K f C in

[0037] In the formula: S i The concentration of adsorbed nitrogen (mg / kg); K f Freundlich constant (mg) 1-n (m 3 ) n / kg); n is an empirical index, C i Dissolved nitrogen concentration in rainwater (mg / m³) 3 ); i refers to a certain pollutant.

[0038] The diffusion control equation is:

[0039]

[0040] In the formula: α is the mass transfer coefficient (1 / s); S eq t is the concentration of adsorbed nitrogen (mg / kg) when adsorption reaches equilibrium, and t is time (h).

[0041] According to the literature "Denitrification behavior and microbial community spatial distribution inside woodchip-based solid-phase denitrification (W-SPD) bioreactor for nitrate-contaminated water treatment" (Jiamin Zhao, Chuanping Feng, Shuang Tong, Nan Chen, Shanshan Dong, Tong Peng, Shunlong Jin. Bioresource Technology, 2018, 249:869-879), the carbon and nitrogen release kinetic equations mentioned include, but are not limited to, zero-order reaction kinetic equations.

[0042]

[0043] In the formula: const is a constant, the value of which is determined by the properties of the material itself.

[0044] Step 3: Connect a continuously stirred tank reactor (CSTR) in series at the outlet of the last sub-unit to receive the water and nitrogen pollutants discharged from the bioretention facility during the entire rainfall process. No kinetic equations are added to this CSTR.

[0045] Step 4: Input the characteristic parameters of the bioretention facility, including cross-sectional area A, packing density ρ, packing porosity θ, usage ratio of each packing material, height of each packing layer, adsorption characteristic parameters of each packing material for nitrogen pollutants, influent flow rate Q and nitrogen pollutant concentration, and nitrogen pollutant concentration accumulated in the packing material during the previous rainfall. Use AQUASIM software to solve for the spatiotemporal variation of nitrogen pollutants in the bioretention facility (i.e., variation with time and variation with bioretention facility height) and the average nitrogen concentration (Event Mean Concentration, EMC) of the effluent under the set rainfall duration.

[0046] The nitrogen removal efficiency (RE) of the bioretention facility is:

[0047]

[0048] In the formula, C0 is the influent nitrogen pollutant concentration (mg-N / L), C e The average nitrogen concentration (mg-N / L) in the first fully mixed reaction unit.

[0049] The influent flow rate Q of the bioretention facility is determined by the service area of ​​the bioretention facility, rainfall, rainfall duration, and underlying surface properties.

[0050]

[0051] In the formula, F represents the service area of ​​the bioretention facility (m²). 2 ); V is the runoff coefficient; h is the rainfall (mm); T is the duration of a single rainfall event (h); V W The amount of water treated by a bioretention facility per rainfall event (m³) 3 ).

[0052] The amount of nitrate (i.e., nitrogen pollutant) accumulated in the non-flooded area of ​​the bioretention facility due to adsorption and aerobic metabolic pathways of microorganisms during the previous rainfall was:

[0053]

[0054] In the formula, The initial concentration of adsorbed nitrate (mg / kg); The influent ammonia nitrogen concentration (mg-N / m³) 3 ); The concentration of ammonia nitrogen in the effluent (mg-N / m³) 3 ); ρ is the packing density (kg / m³) 3 );V s The packing volume (m³) 3 θ is the porosity of the packing material, Q is the inflow rate of the previous rainfall, and T is the duration of the previous rainfall.

[0055] Step 5: For the submerged area of ​​the bioretention facility, a second completely mixed reaction unit is established. The Michaelis-Menten equation and first-order reaction kinetic equation are set to simulate the nitrogen degradation process of microorganisms under anoxic conditions. The average concentration of nitrogen pollutants in the submerged area obtained in Step 4 is used as the initial value of the variable. The nitrogen concentration changes in the submerged area of ​​the bioretention facility under different drought conditions are calculated using AQUASIM software.

[0056] The Michaelis-Menten equation is:

[0057]

[0058] In the formula, C NO3 Nitrate concentration (mg-N / m 3 );V max Maximum reaction rate (mg-N / L / h); K NO3 C is the half-saturation constant of nitrates; DOC Dissolved organic carbon concentration (mg C / m³) 3 ); K C is the half-saturation constant of soluble organic carbon.

[0059] The first-order reaction kinetic equation is:

[0060]

[0061] In the formula, k is the first-order reaction kinetic constant.

[0062] The amount of nitrogen pollution accumulated in the flooded area is variable. The concentration of nitrogen pollution accumulated by the previous rainfall is calculated in step 5. That is, the accumulation in the flooded area can only be calculated after simulating the previous rainfall and then used in the simulation calculation of the next rainfall.

[0063] Example: Predicting the denitrification efficiency of a wood chip-pyrite stratified bioretention facility under different operating conditions

[0064] like Figure 1As shown, a layered bioretention facility consisting of wood chips and pyrite comprises a 0.2m high water storage layer, a 0.3m high non-submerged layer, a 0.3m high submerged layer, and a 0.1m high drainage layer. The non-submerged layer is filled with 90% quartz sand and 10% wood chips by volume, while the submerged layer is filled with 85% quartz sand and 15% pyrite by volume. The drainage layer is equipped with perforated drainage pipes and covered with pebbles to ensure smooth drainage. The drainage pipe outlet at the bottom of the bioretention facility is raised 0.4m to ensure the entire pyrite layer is submerged. Key parameters of the facility, obtained through experimental testing, are detailed in Table 1.

[0065] Table 1 Key parameters of the wood chip-pyrite stratified bioretention facility

[0066]

[0067]

[0068] Step 1: In the AQUASIM software, set up two infiltration sub-units connected in series. The first sub-unit corresponds to the non-submerged layer with a height of 0.3m. The second sub-unit corresponds to the submerged layer + drainage layer with a height of 0.4m. The fluid dispersion coefficient in both sub-units is set to 0. The convection-dispersion equation is used to simulate the infiltration process of nitrogen pollutants in rainwater in each infiltration sub-unit of the bioretention facility.

[0069] Step 2: Add relevant equations for the adsorption kinetics of nitrate by quartz sand to the first-level sub-unit, expressed by Equations 1 and 2:

[0070]

[0071]

[0072] The carbon release kinetics equation for wood chips is also added, expressed by Equation 3:

[0073]

[0074] Step 3: Create a fully mixed reaction unit in the AQUASIM software and connect it in series with the second-stage infiltration subunit. This fully mixed reaction unit does not have kinetic equations added and is only used to collect rainwater and nitrogen pollutants discharged from the second-stage infiltration subunit.

[0075] Step 4: Input the facility characteristic parameters of the bioretention facility according to the data in Table 1; input the influent pollutant concentration according to the underlying surface pollution status in Table 2; simulate the rainfall duration as 2 hours and the rainfall as 20 mm.

[0076] Table 2 Concentration of pollutants in influent to bioretention facilities

[0077]

[0078] Assuming the packing material is effective against NH4 + The adsorption capacity is higher than the influent load, and the NH4 adsorbed in the non-submerged zone is also higher. + During the drought period, the adsorbed nitrate can be completely converted into nitrate by microorganisms. Therefore, the concentration of adsorbed nitrate accumulated in the non-flooded area can be calculated by formula 4.

[0079]

[0080] The influent flow rate Q of the facility is calculated using formula 5, where F is taken as 20. Take 0.7, the rainfall h is taken as 20mm, and T is taken as 2h.

[0081]

[0082] The spatiotemporal distribution of nitrates within a bioretention facility under a given rainfall duration was determined using AQUASIM software, such as... Figure 2 As shown. Figure 2 In (a), at the end of the rainfall, the concentration of nitrate in the flooded area was almost equal to that in the influent. Figure 2 In (b), DOC released from sawdust in the non-submerged zone seeps into the submerged zone with the water, and the DOC concentration decreases with increasing submerged zone depth. The DOC in the submerged zone can be used for heterotrophic denitrification during the dry season.

[0083] Step 5: Create another independent fully mixed reaction unit in AQUASIM software to simulate the microbial degradation of nitrogen pollutants in the bioretention facility flood zone during the drought period.

[0084] The kinetic equation for autotrophic denitrification driven by pyrite is expressed as a first-order reaction kinetic equation as follows:

[0085]

[0086] Simultaneously, a heterotrophic denitrification kinetic equation is added, expressed using the Michaelis-Menten equation as follows:

[0087]

[0088] according to Figure 2 The concentration distribution of nitrate and DOC in the flooded area was analyzed. The average concentrations of nitrate and DOC in the flooded area were calculated, and these were used as initial values ​​for the variables. Software was then used to calculate the degradation of pollutants under a 3-day drought period. Figure 3As shown, at low influent concentrations, the nitrate concentration decreases most rapidly, with DOC remaining at the end of the reaction. Simultaneously, autotrophic denitrification also participates in nitrate removal, while Fe(III) and sulfate continuously increase as the reaction proceeds. At medium influent concentrations, the nitrate removal rate decreases, with no DOC remaining at the end of the reaction, but more Fe(III) and sulfate are produced. When the influent concentration increases further, nitrate cannot be completely removed. Due to insufficient DOC, more pyrite is used for nitrate reduction, leading to a further increase in Fe(III) and sulfate concentrations in the water.

[0089] The calculation results can be used as the accumulation value of pollutants in the flooded area for simulating the denitrification efficiency of the next rainfall event.

[0090] The denitrification efficiency of the wood chip-pyrite stratified bioretention facility under three different influent concentrations is as follows: Figure 4 As shown in (a), when the influent nitrate concentration is at a medium or low level, the denitrification efficiency of the bioretention facility reaches more than 70%, but when the influent concentration is very high, the removal capacity of the bioretention facility is significantly reduced.

[0091] With other parameters kept constant, by varying only the rainfall amount (6mm, 13mm, 26mm) and selecting a specific influent concentration level, software can be used to calculate the nitrogen removal performance of the bioretention facility under different rainfall amounts. The results are as follows: Figure 4 As shown in (b), the nitrogen removal rate of the bioretention facility can reach more than 90% for light rainfall (6mm-13mm); however, the nitrogen removal rate decreases for heavier rainfall.

[0092] As can be seen from this embodiment, the invention provides a rapid and accurate method for predicting the denitrification efficiency of stratified bioretention facilities, which can provide a basis for improving the water purification performance of bioretention facilities.

Claims

1. A method for predicting the denitrification efficiency of a stratified bioretention facility, characterized in that, Includes the following steps: Step 1: Based on the stratification and flooding height of the bioretention facility, set up several in-series infiltration sub-units in the AQUASIM software, and use the convection-diffusion equation to simulate the infiltration process of nitrogen pollutants in rainwater within the bioretention facility. Step 2: Based on the adsorption characteristics of nitrogen pollutants by each packing material in the bioretention facility, adsorption isotherms and diffusion control equations are set in the corresponding sub-units to simulate the dynamic adsorption process of nitrogen pollutants by the packing material. Based on the characteristics of each packing material in releasing organic carbon and nitrogen, carbon release and nitrogen release kinetic equations are set in the corresponding sub-units to simulate the carbon release and nitrogen release process of the packing material. Step 3: Connect a fully mixed reaction unit in series at the outlet of the last sub-unit to receive the water and nitrogen pollutants discharged from the bioretention facility during the entire rainfall process. Step 4: Input the characteristic parameters of the bioretention facility, including cross-sectional area A, packing density ρ, packing porosity θ, usage ratio of each packing material, height of each packing layer, adsorption characteristic parameters of each packing material for nitrogen pollutants, influent flow rate Q and nitrogen pollutant concentration, and nitrogen pollutant concentration accumulated in the packing material during the previous rainfall. Use AQUASIM software to solve for the spatiotemporal variation of nitrogen pollutants in the bioretention facility and the average nitrogen concentration in the effluent under the set rainfall duration. It also includes step 5, establishing a second completely mixed reaction unit for the submerged area of ​​the bioretention facility, setting up the Michaelis-Menten equation and first-order reaction kinetic equation to simulate the degradation process of nitrogen by microorganisms under anoxic conditions; using the average concentration of nitrogen pollutants in the submerged area obtained in step 4 as the initial value of the variable, and using AQUASIM software to calculate the concentration change of nitrogen pollutants in the submerged area of ​​the bioretention facility during the drought period. The Michaelis-Menten equation is: In the formula, Nitrate concentration (mg-N / m 3 ); The maximum reaction rate (mg-N / L / h); is the half-saturation constant of nitrate; Dissolved organic carbon concentration (mg C / m³) 3 ); is the half-saturation constant of soluble organic carbon; t is time (h); The first-order reaction kinetic equation is: In the formula, k is the first-order reaction kinetic constant; In step 4, the concentration of nitrogen pollutants accumulated in the flooded area by the previous rainfall is calculated in step 5; the amount of nitrogen pollutants accumulated in the non-flooded area by adsorption due to the previous rainfall is: In the formula, The initial concentration of adsorbed nitrate (mg / kg); The influent ammonia nitrogen concentration (mg-N / m³) 3 ); The concentration of ammonia nitrogen in the effluent (mg-N / m³) 3 ); Packing density (kg / m³) 3 ); The packing volume (m³) 3 ); Where is the porosity of the packing material, and Q is the inflow rate (m³) of the previous rainfall. 3 / h), where T is the duration (h) of the previous rainfall.

2. The method for predicting the nitrogen removal efficiency of a stratified bioretention facility according to claim 1, characterized in that: in In step 1, the convection-diffusion equation is: In the formula, Dissolved nitrogen concentration in rainwater (mg / m³) 3 ); x represents the depth of the packing layer in the bioretention facility (m); D is the average pore water velocity (m / h); D is the fluid dispersion coefficient (m). 2 / h).

3. The method for predicting the nitrogen removal efficiency of a stratified bioretention facility according to claim 2, characterized in that: in In step 2, the adsorption isotherm is the Freundlich isotherm: In the formula: The concentration of adsorbed nitrogen (mg / kg); Freundlich constant (mg) 1 -n (m 3 ) n / kg); n is an empirical index. Dissolved nitrogen concentration in rainwater (mg / m³) 3 ); i refers to a specific pollutant; The diffusion control equation is: In the formula: The mass transfer coefficient is 1 / s; It is the concentration (mg / kg) of adsorbed nitrogen when adsorption reaches equilibrium.

4. The method for predicting the denitrification efficiency of a stratified bioretention facility according to claim 3, characterized in that: in In step 2, the carbon and nitrogen release kinetic equations are zero-order reaction kinetic equations: In the formula: const is a constant, the value of which is determined by the properties of the material itself.

5. The method for predicting the nitrogen removal efficiency of a stratified bioretention facility according to claim 4, characterized in that: in In step 4, the influent flow rate Q of the facility is: In the formula, F represents the service area of ​​the bioretention facility (m²). 2 ); is the runoff coefficient; h is the rainfall (mm); T is the duration of a single rainfall event (h); The amount of water treated by a bioretention facility per rainfall event (m³) 3 ).

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